Superconductivity in Mo5GeB2 with a tetragonal structure

Abstract The discovery of 39 K superconductivity in MgB 2 and the recent observations of high- T c superconductivity in the high-pressured hydrides motivate ones to search for new superconductors in the compounds containing H or B light element. In this article, we chose the heavier Ge to replace the Si in the ternary borides Mo 5 SiB 2 with the Cr 5 B 3 type tetragonal structure, a relative new group borosilicate superconductors, and prepared Mo 5 GeB 2 polycrystalline sample. By the combination of resistivity, magnetization, and specific heat measurements and band calculations, we determine its superconducting parameters. It was found that Mo 5 GeB 2 is a type II superconductor, with the critical temperature T c = 5.4 K, and the Ginzburg–Landau (GL) parameter k GL (0) = 4.2. The estimated electron-phonon coupling constant λ ph (0.57) and the specific heat jump △ C e l / γ n T c (1.33) demonstrate that Mo 5 GeB 2 is a weak-coupling, single-gap phonon-mediated superconductor. Band calculations reveal that Mo 5 GeB 2 has a similar density of state (DOS) near Fermi energy to that of Mo 5 SiB 2 with the same T c , but smaller than that Mo 5 PB 2 with T c = 9.2 K.